Recent research into the mechanisms of thrombosis during acute coronary syndromes and arterial revascularization procedures (e.g., percutaneous transluminal coronary angioplasty; PTCA) indicates a major role for tissue factor (TF) in the generation of arterial mural thrombi and fibrin. Sources of this TF include soft lipid core, macrophages, and possibly smooth muscle cells (SMCs). Recent in vitro data, however, make a strong case that interstitial vesicles derived from dysfunctional endothelial cells (ECs) may be an additional source in the local disturbed, slow flow regions characteristic of branch points and bifurcations. Such ECs may also directly activate SMCs to produce TF, since in vivo at least some SMCs of atherosclerotic lesions express TF. We will therefore test the hypothesis that ECs control the accumulation of TF in atherosclerotic plaques. Two ways in which this may be true are EC release of TF into subendothelium, and EC activation of underlying SMCs to express TF. Specific Aim 1 is to characterize the functional expression of TF by porcine aortic ECs preconditioned in a flow chamber to low levels of shear stress, without or with hypoxia, and without or with oscillatory shear stress, for periods up to 24 hours. Specific Aim 2 is to extend our findings to a coculture system comprised of a monolayer of porcine aortic ECs overlying SMCs. Specific Aim 3 is to perform parallel studies of TF expression with segments of porcine aorta, also in a flow device. These aims will incorporate factor Xa generation and binding, assessment of TF antigen and gene expression, and, following controlled balloon injury to cocultures and aortic segments in vitro, quantification of platelet adhesion/aggregation by epifluorescence videomicroscopy and/or 111-indium (tropolone)-labelled platelets and 125-iodine-labelled fibrinogen. A clearer understanding of shear stress-conditioned ECs may prove important in the development of specific inhibitors of TF or factor Xa, and in the EC repopulation of lesions induced by such procedures as PTCA.